The induction of pup-killing by olfactory bulb removal in female mice can be eliminated by the administratiion of chlordiazepoxide. In addition to the elimination of pup-killing, a significant number of chlordiazepoxide-treated animals began to exhibit maternal behavior. Pup-killing cannot be blocked, however, by giving 1-day old young to a bulbectomized female in the process of exhibiting maternal activities toward 14-day olds (bulbectomized female mice are normally responsive toward 14-day old or older young. It was also found that peripherally- induced anosmia (infusing zinc sulfate through the nares) also leads to a loss of maternal behavior. Maternal behavior can also be eliminated and pup-killing induced by injecting female mice with either testosterone propionate or estradiol benzoate. Animals so treated stop building brood nests in response to pregnancy, progesterone treatment, or the presence of young. Finally, the reaction of female mice toward young varies as a function of age. Twenty-two day olds ignore newborn young completely whereas approximately 45 percent of 32- and 42- day olds kill 1-day olds (the remainder continue to ignore 1-day olds). However, by Day 62 of life, approximately 85 percent of the females behave in a maternal fashion.